1. Field of the Invention
The present invention is related to a prosthetic bone implant made of a hardened calcium phosphate cement having an apatitic phase as a major phase, and in particular to a prosthetic bone implant comprising a dense cortical portion bearing the majority of load and a porous cancellous portion allowing a rapid blood/body fluid penetration and tissue ingrowth.
2. Description of the Related Art
It is advantageous if a prosthetic bone implant is bioresorbable and is supportive at the same time. Accordingly, an article made of calcium phosphate will be preferable than that made of a metal, if the former has strength which is comparable to a human cortical bone. One way of making such a bone implant is by sintering a calcium phosphate powder, particularly a hydroxyapatite (HA) powder, into a block material at a temperature generally greater than 1000° C. Despite the fact that the high temperature-sintered HA block material has an enhanced strength, the bioresorbability of the material is largely sacrificed, if not totally destroyed, due to the elimination of the micro- and nano-sized porosity during the sintering process.
The conventional spinal fusing device is composed of a metallic cage and a bioresorbable material disposed in the metal cage, for example the one disclosed in U.S. Pat. No. 5,645,598. An inevitable disadvantage of this fusion device is the sinking of the metallic cage sitting between two vertebrae to replace or repair a defect spinal disk, because the hardness and the relatively small size of the cage wear out or break the bone tissue, and in particular the endplate of the vertebra.